Method for preparing aniline by continuously reducing nitrobenzene

Abstract

The invention discloses a method for preparing aniline through continuous reduction of nitrobenzene, belongs to the technical field of fine organic synthesis, and can solve the problems that a catalyst preparation process is complicated and a large amount of by-products such as waste acid are generated by a traditional stoichiometric reducing agent in the existing aniline synthesis process. According to the invention, an efficient continuous reduction system is developed, the reduction system is constructed by H2 / NaBH4 / NiCl2. 6H2O, and the product aniline is obtained at an excellent yield under the conditions of normal pressure and room temperature. The method has the advantages of continuous process, mild reaction conditions and the like, and has industrial application prospects in the field of aniline preparation.

Description

Technical Field

[0001] The invention belongs to the technical field of fine organic synthesis, and particularly relates to a method for preparing aniline by continuously reducing nitrobenzene. Background Art

[0002] Aniline is a very important organic raw material, widely used in dyes, medicines and pesticides. Traditionally, aniline is mainly prepared by reducing nitrobenzene with a stoichiometric reducing agent, such as iron powder and zinc powder. The traditional aniline production process is not only costly, but also produces a large amount of industrial wastewater that is difficult to treat, resulting in serious The selective hydrogenation of nitrobenzene to produce aniline is an environmentally friendly and clean production route. Hydrogenation reduction is divided into gas-phase nitrobenzene hydrogenation and liquid-phase nitrobenzene hydrogenation. Among them, the liquid-phase nitrobenzene hydrogenation process has become the most commonly used method for producing aniline due to its low reaction temperature and few by-products.

[0003] The literature (Pd / rGO catalyzed solvent-free hydrogenation of nitrobenzene to aniline, Fine Chemicals, 2022, 39(1): 127-134) reported that three Pd-based catalysts Pd / GO, Pd / rGO and Pd / C-HNO3 were prepared by using graphene oxide (GO), reduced graphene oxide (rGO) and activated carbon (C-HNO3) activated by nitric acid to load Pd nanoparticles. Among them, the efficient network structure of rGO nanosheets and the good coupling between Pd nanoparticles led to the highest Pd metal specific surface area and dispersion. The reaction was carried out at a Pd / rGO mass concentration of 10 g / L, 1 MPa and 90°C. The literature (Response Surface Methodology Optimization of Nitrobenzene Hydrogenation to Aniline over Pillared Amorphous Ni-B Alloy, Chemical Technology and Development, 2021, 50(8): 21-26) reported that the optimal process conditions for the hydrogenation of nitrobenzene to aniline using amorphous Ni-B alloy pillared bentonite as catalyst were: reaction time 129 min, reaction temperature 114 °C, hydrogen pressure 2.0 MPa, catalyst dosage 1.9%, and the yield of the corresponding product aniline was 90.11%. The literature (Selective hydrogenation of nitrobenzene to synthesize aniline over Ni-Mo-P-EG amorphous catalyst, Fine Chemicals, 2014, 31(6): 722-732) prepared an amorphous Ni-Mo-P-expanded graphite (EG) catalyst by impregnation chemical reduction. The catalyst reacted for 90 min at a reaction temperature of 110 °C and a hydrogen pressure of 1.8 MPa. The conversion rate of nitrobenzene and the selectivity of aniline could reach 99.5% and 99.9%, respectively. Patent CN202210345213.2 discloses a preparation method for a catalyst for hydrogenation of nitrobenzene to synthesize aniline. The method uses nitrobenzene as a raw material and hydrogen as a reducing agent. In the presence of a non-precious metal supported palladium catalyst, in a reaction medium, the hydrogen pressure is 1-10 bar, the reaction temperature is 0-30 °C, and the reaction is carried out in a closed container for 0.5-5 h to convert nitrobenzene into aniline. The above methods can all produce aniline in excellent yields, but the reaction conditions are harsh and usually require heating or pressurization. In addition, the catalyst preparation process is relatively cumbersome. Therefore, the development of a new reduction system for the high-activity hydrogenation of nitrobenzene to aniline is an urgent need and challenge to be addressed. Summary of the invention

[0004] The present invention aims at the disadvantages of the existing aniline synthesis, such as harsh reaction conditions, cumbersome catalyst preparation, and long process flow, and provides a method for preparing aniline by continuous reduction of nitrobenzene. The method has the advantages of continuous process, mild reaction conditions, and high yield, and has industrial application prospects in the field of preparing aniline.

[0005] The present invention adopts the following technical solution: A method for preparing aniline by continuous reduction of nitrobenzene comprises the following steps: In the first step, nitrobenzene, NaBH4, NiCl2·6H2O and reaction solvent are added into the storage tank in sequence; The second step is to adjust the pressure reducing valve of the hydrogen cylinder, set the partial pressure to 0.1 MPa, and set the gas flow rate to 100 L / h; The third step is to set the reaction liquid temperature to 25°C, pass hydrogen into the micro-nano bubble generator to react with the reactants, and the reaction liquid enters the reactor through a peristaltic pump, and then the reaction liquid circulates between the reactor and the micro-nano bubble generator, and the reaction time is 60 min; The fourth step is to filter the reaction solution after the reaction is completed, extract and separate the filtrate to obtain an organic phase, which is then concentrated under reduced pressure and then subjected to column chromatography to obtain high-purity aniline.

[0006] Furthermore, the molar ratio of nitrobenzene, NaBH4, and NiCl2·6H2O in the first step is 1:(0.5~1):(0.5~1).

[0007] Furthermore, the reaction solvent in the first step is methanol or ethanol, and the amount used is 500 mL.

[0008] Furthermore, the eluent for the column chromatography in the fourth step is a mixture of petroleum ether and ethyl acetate in a volume ratio of 20:1.

[0009] The beneficial effects of the present invention are as follows: The present invention develops an efficient continuous reduction system, which is constructed by H2 / NaBH4 / NiCl2·6H2O, and obtains the product aniline with excellent yield under normal pressure and room temperature conditions. The method has the advantages of continuous process and mild reaction conditions, and has industrial application prospects in the field of preparing aniline. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is the equation for the synthesis of aniline by reduction of nitrobenzene of the present invention; Figure 2 The schematic diagram of the device for synthesizing benzoic acid by oxidation of benzaldehyde of the present invention; Figure 3 is the hydrogen spectrum of the product aniline of the present invention ( 1 H NMR); Among them: 1-hydrogen cylinder; 2-micro-nano bubble generator; 3-reactor; 4-peristaltic pump; 5-storage tank. DETAILED DESCRIPTION

[0011] In order to make the purpose, technical scheme and advantages of the present invention more clear, the specific embodiments of the present invention are described in detail, but are not limited thereto. The raw materials used in the embodiments are all common commercial products unless otherwise specified; the methods used are all commonly used methods in the art unless otherwise specified.

[0012] Example 1 Weigh 20 mmol, 10 mmol, and 10 mmol of nitrobenzene, NaBH4, and NiCl2·6H2O, respectively, dissolve in 500 mL of ethanol and place in a storage tank. Enter the reactor through a peristaltic pump, and the reaction liquid circulates between the reactor and the micro-nano bubble generator. React for 60 min at room temperature and normal pressure. After the reaction, filter the reaction liquid first, extract and separate the filtrate to obtain the organic phase, then concentrate under reduced pressure, and then chromatograph on a silica gel column (eluent is V 石油醚 / V 乙酸乙酯 =20:1) to give 19 mmol of aniline with a yield of 95%.

[0013] 1 H NMR (600 MHz, CDCl3) δ 8.14 (d, J = 6 Hz, 2H), 7.62 (t, J = 6 Hz, 1H),7.49 (t, J = 6 Hz, 2H).

[0014] Example 2 Weigh 20 mmol, 10 mmol, and 20 mmol of nitrobenzene, NaBH4, and NiCl2·6H2O, respectively, dissolve in 500 mL of methanol and place in a storage tank. Enter the reactor through a peristaltic pump, and the reaction liquid circulates between the reactor and the micro-nano bubble generator. React for 60 min at room temperature and normal pressure. After the reaction is completed, filter the reaction liquid first, extract and separate the filtrate to obtain the organic phase, then concentrate under reduced pressure, and chromatograph on a silica gel column (eluent is V 石油醚 / V 乙酸乙酯 =20:1) to give 17 mmol of aniline with a yield of 85%.

[0015] 1 H NMR (600 MHz, CDCl3) δ 8.14 (d, J = 6 Hz, 2H), 7.62 (t, J = 6 Hz, 1H),7.49 (t, J = 6 Hz, 2H).

[0016] Example 3 Weigh 20 mmol, 20 mmol, and 10 mmol of nitrobenzene, NaBH4, and NiCl2·6H2O, respectively, dissolve in 500 mL of ethanol and place in a storage tank. Enter the reactor through a peristaltic pump, and the reaction liquid circulates between the reactor and the micro-nano bubble generator. React for 60 min at room temperature and normal pressure. After the reaction, filter the reaction liquid first, extract and separate the filtrate to obtain the organic phase, then concentrate under reduced pressure, and chromatograph on a silica gel column (eluent: V 石油醚 / V 乙酸乙酯 =20:1) to give 15 mmol of aniline with a yield of 75%.

[0017] 1 H NMR (600 MHz, CDCl3) δ 8.14 (d, J = 6 Hz, 2H), 7.62 (t, J = 6 Hz, 1H),7.49 (t, J = 6 Hz, 2H).

[0018] Example 4 Weigh 20 mmol, 15 mmol, and 10 mmol of nitrobenzene, NaBH4, and NiCl2·6H2O, respectively, dissolve in 500 mL of ethanol and place in a storage tank. Enter the reactor through a peristaltic pump, and the reaction liquid circulates between the reactor and the micro-nano bubble generator. React for 60 min at room temperature and normal pressure. After the reaction, filter the reaction liquid first, extract and separate the filtrate to obtain the organic phase, then concentrate under reduced pressure, and chromatograph on a silica gel column (eluent: V 石油醚 / V 乙酸乙酯 =20:1) to give 18 mmol of aniline with a yield of 90%.

[0019] 1 H NMR (600 MHz, CDCl3) δ 8.14 (d, J = 6 Hz, 2H), 7.62 (t, J = 6 Hz, 1H),7.49 (t, J = 6 Hz, 2H).

[0020] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although detailed description is given with reference to the embodiments of the present invention, those skilled in the art should understand that modifications or equivalent substitutions of the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and should be covered by the protection scope of the claims of the present invention.

Claims

1. A method for preparing aniline by continuous reduction of nitrobenzene, characterized in that: The steps include: In the first step, nitrobenzene, NaBH4, NiCl2·6H2O and reaction solvent are added into the storage tank in sequence; The second step is to adjust the pressure reducing valve of the hydrogen cylinder, set the partial pressure to 0.1 MPa, and set the gas flow rate to 100 L / h; The third step is to set the reaction liquid temperature to 25°C, pass hydrogen into the micro-nano bubble generator to react with the reactants, and the reaction liquid enters the reactor through a peristaltic pump, and then the reaction liquid circulates between the reactor and the micro-nano bubble generator, and the reaction time is 60 min; The fourth step is to filter the reaction solution after the reaction is completed, extract and separate the filtrate to obtain an organic phase, which is then concentrated under reduced pressure and then subjected to column chromatography to obtain high-purity aniline.

2. The method for preparing aniline by continuous reduction of nitrobenzene according to claim 1, characterized in that: The molar ratio of nitrobenzene, NaBH4, and NiCl2·6H2O in the first step is 1:(0.5~1):(0.5~1).

3. The method for preparing aniline by continuous reduction of nitrobenzene according to claim 1, characterized in that: The reaction solvent in the first step is methanol or ethanol, and the amount used is 500 mL.

4. The method for preparing aniline by continuous reduction of nitrobenzene according to claim 1, characterized in that: The eluent for the column chromatography in the fourth step is a mixture of petroleum ether and ethyl acetate in a volume ratio of 20:1.

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